The desire to apply a layer of spattering material onto a target surface is spread over a lot of different technological areas. There are various reasons for apply spattering materials to surfaces, with the most common being the desire to protect the surface against environmental influence or to fulfil aesthetic demands such as the desire to apply certain, often multi-coloured, graphical patterns onto the surface or on certain areas of the surface. The spattering as a process can include or be painting, coating, plating, inking, cladding, varnishing, spraying, sprinkling, texturing, overcoating, colouring, tinting or staining by expelling material to be applied to a target surface from a nozzle means.
The technical areas wherein such painting, spattering, inking, dyeing or coating is desired, range for example from construction work, advertising, amusement, camouflaging, machinery building, road marking, markings on sport grounds, indoor and outdoor wall claddings, car manufacturing, furniture production, etc. Also, a repair of already—at least partially—spattered surfaces which are worn out, damaged, sabotaged, partly replaced, etc. is often required, wherein special care must be taken to achieve a high degree of colour matching and also smooth and optically uniform transitions from the old to the new spattering.
The most common types of spatterings are powder coatings and paint-sprayings by airbrushes or painting guns, but there are many other different types of spatterings like for example sprayed plaster as known from boat construction, sprayed mineral wool, sprayed or gunned concrete, sprayed asbestos, underbody coating as known from cars or other spatterwork. Also sandblasting is a very similar field of the art wherein, instead of covering a surface by spattering material, the surface is eroded by an expelled jet of erosive material with almost analogous principles as used in spattering.
The document FR 2 850 322 discloses a device for printing an image on a large surface that may be held and moved manually and is able to determine position and direction on a surface. The device uses this knowledge of its current position to determine which colour needs to be applied on the surface. This determination is accomplished by matching the determined coordinates and an image stored in a memory of the device. The stored image may then be superimposed to the surface to be painted.
In U.S. Pat. No. 6,299,934, a GPS controlled paint spray system comprises a paint sprayer driver program and a GPS paint sprayer. The GPS paint sprayer includes a GPS receiver, a geographical converter for enabling a user to convert a drawing pattern to geographical locations, a location comparator for detecting a location match between the geographical locations of the drawing pattern and a current GPS-based location, and a spray nozzle to spray paint at matched locations. Said geographical drawing pattern can be marked onto either a field, a wall, or a parking lot.
US 2009/0022879 relates to a method for applying paints or varnishes to large surfaces by means of a displaceable, paint applying device which is controlled in a position-dependent manner. Said device comprises a displaceable part of a real time position measuring system using reference marks.
KR 102006009588 provides a method for controlling an injection position of a painting articulated robot, to automatically operate arm-positions of an articulated robot by remote control so that a painting material exactly injects to an object.
For example in the car industry, the usage of painting robots to paint sheet metal or body parts is common state of the art. The robots for fulfilling such tasks are programmed or taught for that purpose by skilled craftsmen.
In JP 10-264060, a system is provided to perform teaching of movements to a robot arm—by anyone, easily and in a short time—to perform painting by maintaining a painting machine at a right location and attitude, regardless of the skillfulness of a worker. The advancing route of the painting machine is calculated by an image processor, and the location and attitude of the painting machine are calculated by a distance/attitude calculator, based on the output signals of an image sensor and a distance sensor which are together mounted at the tip of a robot arm. In a controller, the control parameter of each axis of the robot arm is outputted to a driving device and the control parameter of each axis of the robot arm, which is moved by the driving device, is stored in a storage device in time sequence, while a feedback control is performed so as to maintain the distance of the painting machine and the painting surface to a prescribed value, to face the painting machine to the painting surface and to move the painting machine along the advancing route.
JP 2006-320825 describes an automatic coating vehicle for painting, e.g. an aircraft, wherein the thickness of the paintwork has to be quite accurate—for once to achieve a sufficient protection of the surface on one hand and to keep the weight of the applied paint as low as possible on the other hand. It includes arm control means to control operation and movement of an arm with an actuator head, and to perform a painting process with respect to a surface to be coated based on the information of the coating area or region stored in a memory means and the attitude and position information of said arm. The position of the vehicle and the head are determined using a GPS, as well as a range finder for measuring a distance between the head and an object.
The document DE 10 2008 015 258 relates to a painting robot for painting motor vehicle bodies by means of a atomizer (also known as nebulizer) for spattering the surface, that is guided by the painting robot. Applying multicolour paint is realized using a paint changer.
FR 2 785 230 refers to a ground logo imprinting technique for graphical reproduction of a drawing reproduced on the ground. The technique traces contours on the ground from a computer driven optical system. The contours traced out are then filled in with jet paint pulverization. The ground logo imprinting technique produces a ground print of a predefined advertising logo or drawing. A stencil, formed by a computer integrated optical system is projected onto the ground and jet paint pulverization is applied to the ground surface.
In KR 100812725 a method for controlling the position and angle of a painting robot is provided to execute painting works at the same spray distance and the progressive speed of a spray target point within an orthogonal painting zone by controlling a spray gun at the proper rotational angular speed, access speed, and separation speed. The goal is to generate a uniform spraying on the surface.
U.S. Pat. No. 5,935,657 discloses a multiple nozzle paint spraying system with two separate banks of spray nozzles. Both banks are supplied by paint from an airless pressurized source, and each individual bank has a shut-off valve to stop the flow of pressurized paint to that respective bank. The entire assembly is mounted on a roller stand which has a pair of arms extending laterally outward. During use, the painter merely activates the paint spray and pushes the apparatus along the wall. The lateral arms maintain the spray nozzles at a fixed distance from the wall, and a coat of paint can be applied to the wall uniformly and quickly.
US 2008/0152807, US 2011/0199431, U.S. Pat. No. 7,350,890 and U.S. Pat. No. 7,922,272 are referring to methods and devices for applying an accurately positioned graphic image on a large contoured surface, such as the body of an aircraft. The apparatus used therein can comprise a rail positioning system to be mounted on a portion of the surface on which the graphic image is to be applied. The graphic image application system is controlled by software to operate a positioning system and a graphic image application system.
The basic principle used in those surface spattering applications is to expel or eject a spattering material such as paint from a nozzle means onto a target surface. To achieve such, there is pressure built up inside or before the nozzle which forces the spattering material out of the nozzle or the spattering material is carried away by a jet of gas or liquid which is ejected through or next to the nozzle. The most common examples for doing so are the ones known from painting guns or airbrushes and the ones known from ink-jet printing.
New ink-jet printer like technology is available to paint with narrow spot sizes of less than one centimeter even from 10 cm distance. Such low divergence expelling techniques allow also spraying without masking, real-time colour mixing or colour changing over the area painted or colour fading from one colour to another.
In cases when the painting tool is handheld or at least partially supported by a guide rail, by a weight compensating arm or the like, one challenge is the control of such a systems in a spattering application as described above.
Applying paint or powder to objects such as walls, industrial structures, manufactured goods like car bodies, large machine parts, aircrafts, etc., as target surfaces is especially difficult in cases where just parts of the surfaces should get painted, for example after repairing or replacing damaged parts or overpainting certain areas only.
Painting a pre-defined pattern such as a logo or an image available as a picture or CAD file, which should be applied to a surface, can be quite demanding. Using an airbrush requires a skilled craftsman, who needs experience and knowledge in the guidance and reliable position and attitude handling of the spattering, painting or powdering tool as well as knowledge of paint viscosity, drying conditions and various other parameters during labour.
In case of repairing or adding paint to already painted surfaces, it can also be quite time consuming to find out the already present colour type and kind as well as its thickness in advance of labour. Also, to buy or self-mix the matching colour requires a skilled worker, in particular when doing so at the worksite.
Non-flat (3D) surfaces are a further challenge as well as sudden interruptions of the target surface which need to be spattered, for example walls to be painted which comprise cables or pipes mounted on the surface which have to be avoided or an aeroplane-body comprising windows which should be excluded from painting.
For the application of spattering material according to a desired spattering data, a spatial referencing of the application-unit with respect to the target surface has to be established. Especially in case of targets with large scales, a spatial referencing of the spattering unit over the whole target range is required to achieve such.